Plan position indicating system



Filed Jan. 2 0. 1944 Sep 951 w. A. HUBER EIAL V 2,

I PLAN POSITION INDICATING SYSTEM- 6 Sheets-Sheet 1 FIG. 1 FIG. 2.

LINE a TRANS- (YER TRANS- PULSE MIT-'I'ER M aoz aoo N j OSCILLO- mac: ER SCOPE INVENTOR. WILLIAM A. HUBER MAX GI NDOFF Sept. 4, 1951 w. A. HUBER ETAL 2,566,332

PLAN POSITION INDICATING Filed Jan. 20, 1944 6 Sheets-Sheet FIG. 5. -I I I I l I 54 OUTPUT or 5-" I OUTPUT OF T27 I oscILu-ron H I g I I I I I I I I I l OUTPUT or s-Ia swap cuans u'r I aurrsn T2 In con: :22

5-: ourvu'r or 5-N4: OUTPUT or no amps: 14

I l l l I T 54 V m u-r mm s-ao L 1 :I TPUT or 20 I SHAPEII T5 I l I as UTPUT or s-2I -I: I:I ouwu-r or I CATHODE sure: I 15 RESISTOR 35a. I no: 3.4. 7

OUTPUT or s-zzl I IOUTPUT or Ta I I I l 5-1 INPUT m ro Tll s-2a-I i ou'rru'r or T32 RANGE MARKER T3! 50 i 1 OUTPUT OF'TII s-uhwmmmmuuuuullmuuummmuuuul OUTPUT or a h l lou1'ru'r or TI2 .25 l OUTPUT or T35 540 OUTPUT OF TI, 5-20 INPUT INTO T36 I I I l I I Y l 5-" INPUT INTO "5 5-27' OU-TPUT OF T3. 1 I" II I. I I I l 5|: E OUTPUT or T5 5-2;

| s-Ia A I OUTPUT or T24 INPUT INTO T3! INPUT INTO m I INPUT INTO I I TUIE 324V l 1H5 INPUT m'ro 1'22 I I' I I mvsumx. v I g WILLIAM A. HUBER Ho 5 I OUTPUT or T22 MAX GINQOI'F hat/Mam Sept. 4, 1951 w. A. HUBER ETAL PLAN POSITION INDICATING SYSTEM riled Jan. 20, 1944 6 Sheets-Sheet 5 m 9 m M I vA f MM 4 w W LEEP ME L I l 1 I I wmu z zomu muwmfll ummfim d B Y n u mu; T10 cub: fl a...

- .u m. w %l- -riL 1 Sept. 4, 1951 w. A. H-UBER EI'ALI 2,566,332

PLAN POSITION INDICATING sys'rsm 6 sheets-sheet 6 Filed Jan. 20, 1944 N .2. ulH F r l I I lllllllllllllllll INVENTOR. WILLIAM A. HUBER MAX GlNpOFF lfforne Y Ohn Ohh HNN 1 new: S p 4.1951

PLAN POSITION INDICATING SYSTEI William A. Huber, Neptune City, and

Lakewood,

In! Gilllloil,

Application January 20, 1944, Saial No. 518,934

' 27 chillc 343-11) (Grantednndertlleaetoflarehi,

1 amended April 3.,

The invention described herein may be manufactured and used by or for the Government for governmental purposes, without the payment to us of any royalty thereon.

This invention relates to radio object-locating systems and more particularly to radio locators utilizing a plan position indicator for furnishing the desired information concerning the location of targets.

Plan position indicators relate to that type of indicators which present a polar coordinate map in terms of range and bearing of all objects visible" to the radar system. This type of indication may be produced by means of a polarized transmitting-receiving antenna array rotated around its vertical axis, and a receiver connected to a cathode ray oscilloscope with a radial sweep synchronously following the rotating antenna. The rotating radial sweep makes an electron beam sweep from the center of a long persistence fluorescent screen of the cathode-ray tube to its outer. edge by starting the radial sweep at the instant of transmittinga radio frequency pulse, the radial distance on the screen of the cathoderay tube is made to represent the range of an object while an angle formed between-a reference line and a radial trace through the center of an echo image is'made to represent the hearing of. an object, or its azimuth, by rotating the radial sweep'about the longitudinal axis of the tube in synchronism and in phase with the rotation of the antenna so that the radial sweep and the axis of the antenna lobe always point in exactly thesame direction. Whena radio frequency pulse from the transmitter strikes an object, some small portion or energy will be reradiated in the direction of the radio locator receiver, and 11: the reflected pulse is sufliciently strong, a distinguishable signal or echo is registered by the receiver. These signals are applied to an intensity grid ora cathode of the cathoderay tube to produce brighteningvof the cathoderay trace tor each echo received. the so-called intensity: modulation, and it results in the echoes appearing as bright circular arcs on the fluorescent screen of the oscilloscope. A target appears asva'smallarc due to the width of the. antenna beam; The radial distance and the angular position ofthecenter of such an arc give respectively the-range andthe azimuth of the targetproducingthis arc. Forobtaining bearing readings. ascalein degrees isusuallyprovided around the periphery of the cathode-ray tube screen with a 0. line pointing to the north, as 1 illustrated in Fig. 10. Some form 01 range scale isalsoprovidedfordeterminingtherangeofa and in other instances it consists of "marker" signals which intensity modulates the cathoderay beam so that they appear as bright circles on the oscilloscope screen.

The name originally given to this apparatus was "Radial Sweep Systems" since it is descriptive of the method used for producing the required result. After'some time, PianPosition Indicator, abbreviated as P. P. I. was adapted as more suggestive of the results accomplished by .such systems. Accordingly. henceforth, the apparatus will be simply referred to as P. P. I. in this specification. I 1

The P. P. I. has the inherent advantage of presenting on the screen of a cathode-ray. tube the true bearing and range of all targets in the plane in which the antenna is rotating. This is illustrated in Fig. 8 which shows a target 800 as it appears on the screen or a P. P. I. oscilloscope "I. This indication isaccomplished in the following manner; when the exploratory pulse'leaves the antenna, the beam of the oathode-ray tube leaves the geometric center of the screen traveling in the same direction as the radiated pulse. Sometime later theecho reaches the receiver and at this instant the output of the receiver intensifies the cathode-ray beam which in turn produces a luminous spot on the screen or the cathode-ray tube; thus, the distance of vthe spot from the center is proportional to range.

To obtain azimuth scanning, the antenna is rotatcd at a uniform angular velocity, and the sweep is made to follow the antenna so that the radial path of the cathode-ray beam and the axis of the antenna lobe continuously point in the same direction; thus the angular position of the spot on the oscilloscope screen represents the true bearing of the object. vAfter completion of the sweep, the cathode-ray beam returns to the of t ub and waits tor. the next exploratory pulse to leavethe antenna. v

Thus, there are two requirements which must becomplied with when this type of indicator is used: thesweep' must start; from the center on itsoutwardradial journey simultaneously with the radiationv 0f the exploratory pulse, and the sweep pathmusthave the direction corresponding to. the direction-oi the radiation. From this itfollowsithat-the pointat which the electron :fluorescent screen k determined by the polar coordinates s,seo,saa

' 3 which are r for range, and angle for bearing. as illustratedin F 8. For the sweep to be linear, the electron beam must move radially at umiorm velocity so that equal segments of the radial trace could represent equal increments of range. 'ihe maximum range reached by the electron beam depends upon the length of time consumed by the sweep for the completion of its radial journey; 'thererore, aiflerent maximum ranges may be obtained by merely changing this time, which is accomplished by changing the slope Of the linear portion of the sweep, as illustrated in Fig. 9. This figure illustrates two series of voltage waves, series A being for short rangeand series B for long range. in Fig. 9, the series A waves reach their maximum amplitude in half of the time required for the series B. Since the range determination depends on the constant velocity of propagation of electromagnetic waves,

' it is obvious that the maximum range of the series A is equal to half of the maximum range of the series B. Thus, plan position indicators may have several ranges available for use, but it must be remembered that, unless one range is a multiple of the other, each change of range necessitates a change of range scale on the grating of the tube.

From the description of the P. P. 1. systems given thus far, it follows that the efiect of a map is produced on the screen of the P. P. I. oscilloscope, and it is a known expedient in the art to superimpose over the screen of the P. P. I. oscilloscope a grid, or a grating, of polar coordinates together with a transparent map of the locality that is being scanned. The map and the grating are ordinarily so oriented that the northsouth line coincides with the 0-180 azimuth line of the superimposed grating, with theviewers position at the center of the screen.

The amount or radar information that can be obtained from a P. P. I. oscilloscope screen is limited by the use made of the elfective area of the cathode-ray screen. As mentioned previously, the conventional P. P. I. oscilloscope utitional P. P. I. display, originates at-the geometric enough for retention of echo images from one revolution of the cathode-ray beam to the other so that there are times when a large sector or the display screen is unexcited; and, tnel'erore, apears in its normal neutral state. 'lms large unexcited sector may be utilized for producing some auxiliary images, if such images can improve the performance of a P. P. 1. system. i he second reason why some additional indications iiiay be producedon a P. P. I. oscilloscope screen relates to the fact that there are many applications of P. P. 1. systems which do not require 360" azimuth scanmng, and where only sector scanmng, such as a 180 sector, is all that is required. -'In the latter case, one half of the screen becomes permanently available for the reproduction or any additional auxiliary signals.

The invention discloses apparatus and methods for utilizing these unexcited sectors on the oscilloscope display screen for providing additional indications and additional radar inrormation which enhances the performance of the entire P. P. I. system'by increasing its accuracy and its versatility.

In order to accomplish this result, the invention provides two sweep circuits for a P. P. I. oscilloscope which make the cathode-ray beam travel alternately first along-one radius, and then along the other radius which is diametrically opposite the first radius; accordingly. two sweep patterns substantially 180" out or space phase appear on the screen of the oscilloscope tube. Because of this result, this type of sweep will be rererred to in this specification as a biradial sweep." The bi-radial sweep, like the single radial sweep used for producing the convencenter of the cathode-ray screen at the instant of transmitting an exploratory pulse, and proceeds radially toward tubes periphery. However, the sweeps forming the bi-radial display are 180" out of space phase, and there is one biradial sweep for two transmitted exploratory pulses, one exploratory pulse starting one sweep,

and the next pulse starting the other sweep.

lizes a sweep which starts at the geometries center of the cathode-ray screen and sweeps linearly with time toward its periphery. The direction the sweep takes when it leaves the cen- This bi-radial sweep makes it possible to display additional indications on the screen of a P. P. I.

terof the screen is controllable and can be in any direction, but in actual operation, in order to obtain true azimuth determinations, the sweep rotates through 360 around the center of. the screen in phase and in synchronism with the antenna array; accordingly, as a rule, the entire area of the cathode-ray screen is scanned. Because of this'rotational sweep through 360, one may be inclined to think that there is no room left on the P. P. 1. screen for any additional indications. This is not necessarily the case in every instance for two reasons. The first reason 7 relates to the rotational speed of the sweep. As

mentioned previously, this speed must be equal to the speed of rotation of the antenna array of the radio locator for obtaining true azimuth readings. The antenna array rotational speeds are ordinarily quite low so that by far the larger portion of the oscilloscope screen appears in its normal, blank state because of the limited retentivity of the screen. Frequently P. P. I. oscilloscopes are used in connection with radar systems the antenna mounts of which are not capable of the rotational speeds greater than one revolution per minute. When this is the case, the retentivity of the display screen is not long oscilloscope in such a manner that, while one type of information appears on one sector of the screen, the additional information appears on the diametrically opposite sector or the same screen. Because of such disposition 'of the two sweeps it becomes possible to utilize two sectors of the oscilloscope screen without producing any image interference of any kind between the two displays.

This type of display widens the possibilities of P. P. 1. systems since it enables one to display on the same screen simultaneously two ranges. Depending upon the adjustment of special oscilloscope circuits, which will be dis losed later on in this specification, it now becomes possible to make both ranges start at zero range, or delay one or both ranges on the oscilloscope screen any desired amount. It thus becomes possible to use one of the radial sweeps as a Vernier tor the other, reproducing any section of the main range Y P.P. 1. system;

amass.

tcilti on'toprovldeanewmethodandapparatus foramoreeii'ectiveutilintionofan sereen'inRRLradioobiecteloca-tingsystems.

Anothcrobiectofourinventionistoprovidea P.P.I.systemwithabi-ra dialsweeposcilloscopewhichenablesonetodisplaysimulm ousLytworangesonthescreenofaslngleP.P.I. oscilloscope tube. These ranges may remain permanentlynxedoroneof-them-mayremain permanently fixed whilethc occurrence of the othersweep ndransama-ybevariedsoasto.

actasavernlerfortherangcthatremainsflxcd.

Btillanotherobjectofthisinventionisto pro,- vide a bl-radial sweep for a P. P.-I. which can be operated either in connection with synchronous radio locators, which are lmder constant control of a oscillator, or in connectionwith self-synchronous radio locators, which are contmlledeitherbyalinepul'semodulatororthe Still anotherobiect scan only the desiredsector at normalangular velocity and at the same time gradually rotate .this sector for obtaining 360 azimuth scanning this beam at controllable intervals so that the range scale appears directly on the screen of an moscope as a series of bright dots.

The novel features which we believe to be characteristic of our invention are set forth with vention itself, however, both as to its organization and method of operation, together with the further objects and advantages thereof, may best be understood by reference to the following description in connection with the accompanying drawings in which:

l 'igurelisablockdlagramoi'asynchronous radio locator;

Figuresisablock diagram oi'a PigureSisablockdiagramofthcbi-radial Figure 4 is a block oscilloscope circuit:

Figure 5 illustrates the of the" waves produced by the various components of 1 the bi radial P. P. I. oscilloscopei Figures 6*and '7 are the schematic diagrams or the bi-radial P. P. 1. oscilloscope;

.Pigures a and 9 are explanatory flgures which -are used to aid the understanding of the invention;

Figure 10 illustrates a'bi-radial sweep reproduced on a screen of an oscilloscope tube and "an azimuth grating surrounding the screen;

of this invention isto ro vide switching arrangements which enable one to use either of the two sweeps separatelyrto diagram of them-rad al systems is called the self-synchronous systems;

views offlthc oscilloscope Figure 10. v y Classification o] the radio object-locating mum Before proceeding with the description of the specific systems and circuits disclosed inthis specification, for the sake of clarity of the disclosure, a broad present day classification of the radio object-locating systems will be given first. The two broad classes of the radio locatbrs are asfollows: one class uses a synchronizing for controlling operatlng periods of transmitting and receiving channels, this oscillator keeping the two channels constantly in the strictest synchronism. This type of system is sometimes called a synchronous system. In the second class of systems the synchronizing os fl lator may be absent altogethenand the synchro-T nous operation of the and receiving channels is accomplished by using either a keying or a transmitting pulse. The latterclass of They ordinarily use the "slave sweep" or "servo sweep" circuits. and spark gap keyers; when spark gap keyers are combined with Marx circuit and Guilleman line, the spark gap keyers are I then called line pulse modulators.

The invention relates to both classes of the rarlio object-locating systems.- Figure 11s a block' diagram of the radio object-locating system of the first class, -i. e. the synchronous system, while Fig. 2- discloses a block diagram of asystem of the second class, i. e. the self-syrichronous system.

Referring to Fig. 1, a synchronizing oscillator II, the frequency of which is adjusted so as to conform with the desired range -of the system, I

generates a sinusoidal wave which is impressed on a keyermodulator l2 comprising aseries of A .shaping' and power amplifiers which transform the sinusoidal wave into a series of powerful voltage pulses of very. short duration occurring particularity in the appended claims. Our inself-synchronous radio locator;

once for each cycle of the sinusoidal wave. The duration of these pulses is ordinarilyof the order of one to three micro-seconds. These are impressed on a transmitter N which is set into ultra high frequency oscillations for the duration of, the keying pulse- The U. H. F. pulse is impressed on a highly directional antenna array it either .directly or through a duplexing circuit ii, the antenna array transmitting one exploratory pulse for each cycle generated by the synchronizing oscillator Hi. It is quite customary in connection withthe P. P. I. systems that the antenna arrays should scan the entire area by' continuously revolving in one direction through 360. However, sector scanning, such as 180 sector, is also possible and will be described more fully,- together with its advantages. later in this specification. If there are any objects within the scanned field of antenna I which are capable of reradiating the transmitted pulse, a small portion of the transmitted energy will be reradiated by these objects in the. direction of the radio locator and will reach antennaarray l8, which at this instant acts as a receiving antenna. The

received energy is impressed on a duplexing circuit II and a receiver. II, the output of which -is impressed on a l. P. I. oscilloscope 22; the

. latter being also connected to the synchronizing Figure 11 illustrates the relationship between Figures} and "I;

Pigurelil is a schematic diagram of a commutator for sector scanning; and

Figures 13 and 14 are detail cross-sectional oscillator Ill. v

For more detailed descriptions of suitable types of transmitter II and keyerll, reference is made.

to applications of James R. Moore, Serial Nos. 467,268 and 467,269 both filed on November 28,

1942, Patent No. 2,464,252. granted March 15,

crating momma aim 7 1949. and Patent No. 2,462,885, granted March 1, 1949, respectively; John W. Marchetti, Serial No. 477.782, filed March 3, 1943. and Melvin D. Baller, Serial No. 477,103, filed February 25. 1943. Patent No. 2,497,854 granted February 21. 1950. For a' more detailed description of suitable types of duplexing circuits, reference is made to an application of L. C. Young and R. M. Pageantitled Impedance Control Coupling and Decoupling System, Serial No. 326,640. filed on March 29, 1940, and an application of A. A. Varela and R. A. Herring. Jr., entitled Antenna Duplexing System, Serial No. 452,534. filed on July 2'7, 1942.

Receiver 29 circuits are well known in the art, and need no detaileddescription or reference. Any U. H. F. heterodyne receiver is suitable for high peak power in the pulses, special switching and timing methods are used, which consist of fgruiodic charging of artificial museum; the when. mtem disclosed in Fig. 1, it has been stated that'synchronization of th entire 'system'depends on the synchronizing oscillator. .Since'there is no synchronizing the purpose at hand..' The oscilloscope 22 circults will be described in great detail in this specification.

The operation'of thesystem is briefly as follows: synchronizing oscillator it controls keyer,

modulator I2 in such a manner that the latter keys transmitter It with a constant predetermined periodicity, this periodicity being controlled by the frequency of the oscillator. Transmitter l4 emits through the polarized directional antenna array I6 periodic pulses which constitute the field exploring signals. If there is a plurality of echo-producin objects within the antenna field, their echoes will appear as a plurality of bright arcs on the screen of the P. P. I. oscilloscope, as illustrated at 890, I908 and Illll in Figs. 8 and 10 respectively. The azimuth of the object is determined by reference to the angular position of a line bisecting the image are on the P. P. I. oscilloscope (angle 0, Fig. 8), while its range is' determined by reference to the linear scale and its distance from the center of they oscilloscope screen (distance 1', Fig. 8). v

Figure 2 illustrates a simplified block diagram of a self-synchronous P. P. L'radio locator. In

this system synchronization of the receiving and transmitting channels is obtained by using thevoltage pulse generated by the keyer or the transmitter in the receiving channel. The keying pulse is generated by a line pulse modulator 200 which may have different degrees of stability depending upon the type of line switch used. The most important advantages of the line pulse modulator and of the self-synchronous systems as compared to the synchronous system, where modulation is obtained from a master oscillator,

resides in the iacts'that the line pulse modulator represents a'much lighter equipment, it is possible to radiate pulses of extremely short duration and greater power by means of th line pulse modulator, and the rate of keying of the transmitter may be very readily changed, which, to gether with some additional changes in the system, results in change of range of the radio 10- cator. In the line pulse modulated systems, the

interval between the pulses is fairly long as com-' pared to the duration of the pulses, and both the repetition rate and pulse duration vary considerably irom. one radar application to another.

Inthe'radio object-locators. the pulse duration is usually of the order of one to two microseconds, and the repetitionrate varies from 60 to 2500 pulses per second. In principle, the line pulse modulation method consists in switching "on" and "oil' the high tension supply to the oscillator so that the valve is "on for the duration not to berestricted to signals which are reflected oscillator in Fig. 2, the entire system in this case is synchronized by means of the voltage generated by th line pulse modulator I" or' the signal or reradiated'by any object. This term is also used to signify any response to a signal such as the one obtained by means ore normally inoperativ' transmitter located on an object which when keyed by the transmitted pulse automaticallysends an answering pulse either on the same or difl'erent frequency.

; Referring now to Fig. 3, which is asimplified block diagram of a P. P. I. system with the biradial sweep P.P. I oscilloscope,'a synchronizing oscillator I09 appears in thecentral left portion of the, block diagram, and the transmitter channel components consisting of a keyer 302 and a transmitter 394 are connected to the synchronizing oscillator 380, and appear directly above the oscillator. The output of transmitter 304 is impressed through a duplexin circuit 306 on a po-v larized antenna array 3. The same antenna array is also connected'through duplexing circuit iii to a receiver III, the output of the latter being impressed on a video amplifier and mixer 3i2.'the purpose of which will be described later in this specification. Antenna array 398 is connected through gears I H on one side to a driving motor lit and on the other side to a seisyn generator 3J9, thethree-phase stator winding of the latter being connected to a receiver seisyn' 329.

Driving motor 6, as well as the generator and receiver selsynsilli and 320 are connected to a common source of alternating current over con- ;ductors 322. Driving motor SIG rotates the antenna array 398 at a constant predetermined speed. and the selsyn generator and receiver 318-320 are used for transmitting the rotational movement of the antenna array to' a rotating electromagnetic deflection coil 322 used for producing rotation and radial sweep oi the cathoderay beam in a P. P. I. oscilloscope tube 324. This electromechanical connection, between the rotating shaft of antenna array "I and rotating coil 322, which also includes a differential gear 326 and driving gears I29 and 9.8.0125 as an interlocking means between the antenna and the cathode-ray beam of the oscilloscope tube 824 so that the cathode-ray beam always iollowsand always points in th same direction 'as antenna I09. In order to point initially the radial beam ,defiection. oi the oscilloscope tube andthe axis of the'pulses and fofi" in the intervalbetween the pulses. On account of the short duration oi the pulse, a relatively high repetition rate, and

of the antenna lobe in the same direction, difiercntial gear 326 is provided with an indexing wheel "I which is used for adjusting the angular posicilloscope.

pressed on a frequency divider 330 consisting of an Eccles-Jordan multivibrator circuit, which generates a series of rectangular waves -0. These are impressed in parallel on two difi'erentiating networks, separators and shapers 340 and I which transform the rectangular waves impressed upon them into two series of rectangular pulses 5-I5 and 5-3. Pulse 5-I5 is used for controlling a multivibrator 3 and saw-tooth oscillator, amplifier and clamper connected to it, while pulse 5-3 controls a precision delayed multivibrator and diflerential network 345 and circuits included in a. block 340. Two saw-tooth waves 5-" and 5-H appearing in the output of the blocks 343 and 343, are impressed on a rotating yoke, consisting of electromagnetic deflection coils 322, where they produce the radial defiection or the cathode-ray beam from the center of the cathode-ray screen alternately in the opposite directions. The precision delayed multivibrator circuit 345 is inserted in the lower sweep generating channel for delaying the appearance of the new control pulses 5- so that the lower channel, generating saw-tooth wave 5-I3, could be adjusted so as to position this saw-tooth wave in any desired time relationship with respect to the transmitted pulse. This enables one to select any desired portion of the full range for reproducing the selected portion on a faster sweep 5-I3.

In order to suppress the cathode-ray beam during the inactive periods, a positive bias is applied to a cathode 312 through a potentiometer arm 314 connected to a bleeder resistor 310. This cathode bias prevents the cathode-ray beam from normally reaching the oscilloscope screen during the return and the inactive periods of the operating cycle. To overcome this bias during the desired active. periods of the sweeps, the outputs of the multivibrator circuits 346 and 348 are connected to an intensity amplifier and mixer 354 which in turn is connected to an intensity grid 356 of tube 324 through a potentiometer 350 To facilitate range determinations, the oathode-ray tube is provided with a special circuit which intensifies its beam at predetermined intervals, thus producing regularly spaced markers I004, Fig. 10, on the screen of the range os- This is accomplished by impressing the output of bufier, phaser, and shaper 332 on an isolating amplifier 330, a range marker 362 and a second isolating amplifier 33. Range marker 302 comprises a short duty cycle free oscillating multivibrator which is time-phase synchronized with the starting periods of the sawtooth waves by means of pulses 5-23 impressed upon it by the isolating amplifiers 360. The output of the range marker consists of a series of uniformly spaced peaked voltage pulses 5-24 which are combined in a video amplifier and mixer 3I2 with the output of receiver 3I0 producing a composite signal 5-30; this is impressed on cathode 312 producing intensity modechoes appearing at I 000, llll and the markers at I000. Sweep I002 to "I2 is a long range sweep, and sweep I002 to Illl is a short range or a vernier sweep.

The operation of the system illustrated in Fig. 3 is as follows: transmitting antenna 300 is pointed directly at north and indexing wheel 330 is used for pointing or aligning the cathode-ray beam so that it sweeps irom the center I002, Fig. 10, tothe point marked 0 on the angular scale of the screen. With this alignment of the antenna array beam and of the coil 322 accomplished, the antenna array beam and the radially deflected cathode-ray beam will then point in the same direction. The system is now ready for operation and the exploratory pulses are transmitted scanning the field by means of antenna 300, which is now made to turn at uniform speed by driving motor 3". Since there is an electro-mechanical connection between the rotating shaft of antenna array 303 and coil 322, the beam of the oscilloscope tube will be following the beam of the antenna array. The sweep circuits are synchronized with the transmitted pulse so that sweeps 5-H and 5-I 3 start the defiection of the beam from its normal central position I002, Fig. 10, toward the periphery oi the screen at the instant oi the transmission of the exploratory pulse. The timing as well as the duration of the sweeps are so adjusted that while sweep 5-" results in the deflection of the beam along one radius (Radius I002-IOI2, Fig. 10) at the instant of transmitting the first pulse, sweep 5-I3 starts the deflection of the beam at the instant of transmitting the second exploratory pulse along the radius which is substantially diametrically opposite the first radius (Radius I002-IOIl, Fig. '10). The signals impressed on cathode 312 of the P. P. I. oscilloscope by receiver 3l0 and amplifier and mixer 3i 2 will be reproduced, therefore, first along one sweep and then along the other sweep on the diametrically opposite sides of the tube, as illustrated at I005,

I000 and IOI0 in Fig. 10, the duration of the sawtooth waves being so adjusted that sweep 5-I3 acts as a vernier sweep for the full range sweep 5-I'I. The occurrence time of the vernier sweep may be varied for reproducing any desired portion of the full range. This mode of adjusting the sweeps is not the only mode of operation that is described in this specification, and other modes of operation and relative adjustments oi. the sweep circuits will be more fully described later, especially in connection with the description of Figs. 6, 'l and 12. As mentioned previously, the cathode-ray tube 320 is normally biased to cut an and the intensity grid 350 overcomes this blocking potential during the linear periods 0! the sweep waves 5-" and 5-I3 without producing any fluorescence on the screen. Because of interference signals, however, some degree of fluorescence is nevertheless present when the blocking potential is removed, and it is this fluorescence that is indicated by the shade lines in Fig. 10. Since a more detailed description of the circuits as well as the functioning oi the oscilloscope circuits appears later in this specification in connection with the description of the 4, 6 and .7, in order to avoid repetition, only the brie! description or the operatitriirg1 cycle given thus far appears suflicient at this e. Reference is now made to Fig. 4, which is a block diagram of the oscilloscope circuit. From the description given thus far, it should be apparent that the'oscilloscope circuit may be conveniently divided into several main components, or channels, whichperi'orm specific. independent functions ofthc operating cycle. Since the P. P. I.

oscilloscope now has two independent sweep cir-' cuits which alternately exert their influence upon the beam or the oscilloscopetube, it is apparent that on must have two independent sweep generatingchannels. channelNo. I generating a long sweep for reproducing the entire range, and No. 2

generating a sweep which is faster but of .equal amplitude. The system disclosed in Fig. 4 will be described in connection with that mode of operation where No. I sweep channel generates a faster sweep, and. therefore. is used as a vernier for No. I sweep channel. However, means are provided for varying the duration of No. 2 sweep so that it can be made either shorter or equal to the duration of No. l sweep. If one is to operate anew through. The resultant negative rectangular voltage pulses Il are used to control the sweep 7 and range marker channels. From the descripchannel, if one is to use it as a vernier device,

tion of the synchronizing pulse shaping channel it follows that it,transforms the sinusoidal output of oscillator 4 into a series oi rectangular diiferentiating networks and the separators, the

the oscilloscope circuit in connection with the synchronous radio locator, circuits must be provided for modifying the sinusoidal wave generated by the synchronizing oscillator into short,

periodic pulses which could be conveniently used for controlling the timing of the two sweep channels. Moreover, additional circuits must be provided for producing the range markers and for suppressing the reproduction of the undesirable of Fig. 4. The P. P. I. oscillompe tube 3241s at the right portion of Fig. 4. There isan identical showing oi. some of the elements in Figs. 3 and 4. When this is the case, they bear the same numeralsinbothfigures. 7

Referring now to a more detailed description of the respective channels, and beginning this delatter comprising diodes, transform the rectangular wave H into a series of positive and negative pulses 5|'and I-l4. A shaping amplifier 43.! in the No. i sweep channel is connected to the plate'of the rectifier so that it is controlled by the negative pulses 5-44, while a shaping amplifier 4l 2"in the No. 2 sweep channel is connected to the cathode oi the rectifier in its channel so that it'is controlled by the positive signals l|. The phase or time'relationships of these signals is clearly indicated in Fig. 5 pthey are separated from each other by one period of the sinusoidal wave 5-l. The shaping amplifiers 430 and 432 transform these pulses into rectangular pulses H and 5-li. Sweep channel No.2 is provided with a precision delayed multivibrator 345 which generates a rectangular wave-I-ll; the duration of the latter may be varied by varying the biasing potential impressed on the control grid of the first tube of the multivibrator circuit. This multivibrator is used in the lower channel, as it may be recalled from the description of Fig. 3, for varying the time of occurrence of the saw-tooth wave genportion of the full range may be reproduced on an expanded scale provided by this channel.

scription with the synchronizing pulse shaping 4l6 where the sinusoidal wave generated by the synchronizing oscillator 41. is eventually utilized for keying the transmitter and for controlling the periodicity of the transmitted exploratory pulses. Phaser 4|! is used for the initial cophasing of the transmitting, receiving and sweep channels so that the full range radial sweeps generated by the No. i sweep channel would always begin simultaneously with the appearance of the transmitted exploratory pulse at cathode "I. Once this cophasing operation has been accomplished, the setting of phaser 4!: remain fixed. The sinusoidal wave appearing in the output of phaser 4l2 is impressed on a shaping amplifier 4 l l which transforms it into a rectangular wave 5-! (these waves may also be found in Fig. 5) and impresses it on a diflerentiating network 42' which in turn transforms them into a series of positive and negative pulses l4. These are impressed on a clipping and shaping amplifier 422 which is biased beyond cut oil. so that the negative pulses are eliminated and only the peaks of the positive pulses get tion of a full range sweep wave 5-" appearing in the output of a sweep generator 438. After "being amplified in a sweep amplifier 44!, the

current saw-tooth wave Sl|a is impressed on the rotating coils 322. A'clamper circuit 446 is provided which stabilizes the'position of the zero range .center point I002, Fig. 10. on the screen of the oscilloscope. No. 2 sweep channel is protooth waves 5i3a and 5-lla are impressed on first in one direction and then in the Opposite direction as illustrated at 5-" in Fig. 5. This produces the bi-radial sweep and deflection of the coils I22. a saw-tooth wave current fiows thecathode-raybeamfirstalongoneradius aw y.

then along the other radius which is diametricallyoppositethe first.

Since the cathode m is nor-many above the ground potential impressed by potentiometer I", over conductor 314, thecathode-ray beam normally does notreach the fluorescent screen of the tube, and, therefore, all undesirable periods of the operational cycle of the tube remain normally suppressed. To reproduce the echoes during the useful portions of the cycle, the intensity grid 356 is connected to a potentiometer .333

description of'Fig. 3.

The composite signal impressed on cathode 312 is illustrated at 6-30 in Fig. 5, and the efi'ect that it produces on the oscilloscope screen is illustrated in Fig. 10. the center of the oscillo-' scope screen being at I002, the marker signals appearin as bright spots I004 and the echoes appearing at I000, i000 and "M. In Fig. 10, sweep I! and I0" is a long range sweep, and sweep I002, I0 is a short range or a vernier range sweep.

- As mentioned previously in connection with the description 'of Fig. 2, the iii-radial sweep oscilloscope circuit is suitable'for operation either with a synchronous radio locator, Fig. 1; or a self -synchronous system i Fig; 2. The alternative connections :for the self-synchronous operation are illustrated in Fig. 4 by the conductor 334 and the switches, 33! and 331. These connections have been already described in connection with the Pigs. 2-and. 3. 1 I

Referring now to Figs. 6 and 7, the relationship amplifiers T4 and ,T-3. the output a: thelatier transformer .02 634 to keyer i2. Pig. 1 where it is eventually utilized for periodic keying of transmitter II. The output of butter amplifier T ,I is connected through a transformer 000 top phase shifter consisting of a variable resistor condenser combination 600, I", a double pole-double throw switch 6", and a centrally tapped secondary of transformer .00. This phase shifter, as it m be recalled from the description of Fig. 4, is used for the initial cophaslng oi the sweep channels 400 and 402.

I The phase shifter-sot this type are well known in the art and do not need any detailed description. The sinusoidal wave appearing in the output of the phase shifter is impressed on a shaping amplifier T4 which is overdriven in both positive and negative directions by the sinusoidal wave. An

approximately rectangularwave 5-3 appearing in its output is impressed on a differentiating network "3-bit where it is transformed into positive and negative pulses 54, which are imof which with respect to each other is illustrated in Fig. 11, these figures being the schematic diagram for the bi-radial oscilloscope. sweep circuit, the disposition of the channels in these figures is as follows: reading from top to bottom of Fig. 6, one has the synchronizing pulse shaping channel 406, the range marker channel 404, and the video amplifier and mixer an; the frequency divider multivibrator 336 appears in' the upper right corner of Fig. 6, and the two sweep channels 400 and 40! appear in the. upper and lower portions of Fig. 7, with the intensity amplifier and mixer 354 appearing in the central portion of Fig. 'l; the oscilloscope tube 324 appears in the right portion of Fig. 7.

Proceeding now with the description of the synchronizing pulse shaping channel 400, it begins with a synchronizing oscillator pentode T l generating the sinusoidal wave Fl. As-in Figs. 3 and 4, the oscillogram numerals in Figs.v 6 and '7 correspond to those of Fig. 5, Fig. 5illustrating' the wave forms as well as the time relationship between the respective osciilograms. Any oscillator circuit may be used for the purpose at hand. and no special frequency stability is necessary in this case since all circuits connected to the oscillator follow the oscillator voltage even though an occasional frequency drift does occur. The output of Tl is impressed in series on two buifer pressed on the control grid of a negatively biased amplifier T-5; the latter eliminates the negative signals and reshapes the positive signals into substantially rectangular negative voltage pulses 5-5. These are impressed in parallel on an Eccles-Jordan multivibratorcircuit consisting of triodes T-t, T|. and on an isolating and inverting amplifier T3, the output ofthe latter being used in the range marker channel 404 which will be described later. The Eccle's Jordan multivibrator circuit is well known in the art and 'does not need any detailed description. It may be remarked parenthetical y nevertheless that it has two degrees'of stability, onetube being fully conductive while the other tube is nonconductive. and vice versa the conductivities of the tubes being controlled by either positive or negative pulses impressed in parallel on their control'grids. Once "put into one state of stability, the circuit remains in this position indefinitely iintil it is put into the other state by the control pulse impressed on the control grids of the two tubes. The voltage signal appearing in the plate circuit of tube T0 is a rectangular wave 5.6. Switch 335 interconnecting trlodes T5 and T-6 corresponds to the same switch in Figs. 3 and 4;- it may be recalled that this switch is used for disconnecting the 0s:-

-cilloscope circuit from the synchronizing pulse shapin channel 400 whenit is desired to use the oscilloscope in connection withthe self-synand. m 'on two diflerentiatingnetworks consistchronous radio locator. When this is the case, the sychronizing voltage signals impressed on the control grids of T 6 and T'-| over conductor 334 come from the 'line pulse modulator 200, Fig. 2.

No inverter amplifier is indicatedin any of the figures between the line pulse modulator 200 and multivibrator 336 since actual experience'indi cated that multlvibrator 336 functioned equally" well when its conductivity positions were controlled either by the positive or negative control signals. However, if it is desired to control it by means of positive signals, aninverter may be inserted-in conductor 334. The rectangular wave H is impressed inparallel over conductors GIG ing of condenser resistance; combinations I03, I05, I00 and HM. Here it istransformed into aseries of positive and negativepulses which are impressed on the plate and cathode of diodes T 0 and T|0 respectively. Diode T- 0 is rendered conductive by the positive pulses and diode T-I 0 is rendered conductive by the negativepulses.

The voltage signal impressed on Y the controlv grid ofT-il is illustrated at't-l. Since the control grid of T-'-ll is coupled to the cathode resistor III of diode T--0, the signals impressed on this grid have positive polarity since thenegative signals have'been by-passed to ground by resista substantially rectangular pulse -0. This is impressed on a potentiometer 100 which is connected to the control grid of atriode T I0 through a coupling condensor 100. Triodes T-l3 and T-il represent a precision delayed multivibrator circuit which is used for generating a rectangular wave Il0 'of adjustable width. This multivibrator comprises a twin triode biased mulaim 122 and H0, and the grid potential of T-ll rises to the point at which TI| begins to conduct. At this point T -i8is cut off and the multivibrator returns to the. quiescent condition. The

change occurs very rapidly and in a' regenerating fashion. with the beginning of the current in T-H the cathode potential rises to cut of! T--l3. which in turn raises-the grid potential of T-- through condenser 120 increasing the current in TIl.

The pulse width can bealtered by changing the values of the resistance 122, condenser 120, resistance 1I2, or the grid potential impressed on .the grid of T-Iil by potentiometer resistance 100. The variation of the grid potential is actually the most convenient method of controlling the pulse width, Its principal eil'ect occurs in changing the cathode potential when T-II' is conducting and thereby changing the amount condenser 120 must discharge before T--I| begins to conduct. It also varies the plate voltage of TI3 when the latter is conducting. It may be shown experimentally as well as theoretically that this, together with the curvature of the gridtivibrator, the width of the output pulse of which is a linear functionof the grid bias impressed on the grid of the firsttriode TI3 by a biasing battery 101 and a potentiometer 100 through a grid resistor 1I0. Potentiometer 100 comprises that source of variable biasing potential which is used for controlling the width of the rectangular wave 5ll appearing in the output circuit of triode TI3. The common cathode of the triode is connected to ground over a cathoderesistor 1i! and the plates are connected to a positive source of potential 1 over resistances H6 and H0.

The grid of triode T-ll is coupled to the plate of triode TI3 over a condenser 120, and to the positive source of potential I I4 overa resistance 12:. v v

The operation of this multivibrator circuit is as follows: normally, the second triode T-Il is conductive since this grid is held at approximately the cathode potential by the grid current through the large grid resistance 122. The voltage drop through the common cathode resistance H2 is suilicient to make the cathode positive with respect to the grid of th e first triode T-I3 which is, therefore, nonconductive. Condenser 120 is charged to a voltage equal to a potential difierence between the plate of T-II and the grid of T-Il because of the small grid current drawn by T-Il. A positive trigger voltof the trigger signalpasses into the grid circuit.

A diode may be used between T-il and T-Il to insure that the voltage applied to the grid is positive. A positive trigger of about 0.2 microsecond results and T-I8 thereby becomes conductive. The plate voltage of TI0 drops. a d a through condenser 120 the grid of T-Il is driven below the new cathode potential. The cathode potential falls immediately after the trigger pulse v plate characteristic of T-I3, results in a high degree'of compensation of the inherently nonlinear relationship between the voltage and discharge time of condenser 120. Because of the highly accurate linear relationship between the pulse width and the grid voltage, the multivibrator composed of the tubes T and .T-ll is here referredto as a precision delayed multivibrator. This highly'accurate linear relationship between the pulse width or the duration of the duty cycle of this multivibrator and the grid voltage is utilized for changing the time of occurrence of the saw-tooth wave generated by the No. 2 sweep channel and for determining the range up to that point at which the vemier range begins. Therefore,vthe range reading in this case consists of the range reading as it appears on the calibrated scale of potentiometer plus the reading of the vernier sweep. Moreover, the calibrated potentiometer 100 is used forquickly selecting the desired portion of the full range for its reproduction on the Vernier range.

The rectangular wave 5-10 is impressed on a differentiating network -426, which transforms it into a series of positive and negative pulses 5I I. These are impressed on the control grid of the first tube of a second delayed multivibrator circuit consisting of triodes T-IS and T-I6; the connections and the functioning of which is identical to those of the precision delayed multivibrator TI3, T-'-I4 with two exceptions: the biasing potential impressed on the control grid of TI5 remains fixed. while the time constant of a resistance-condenser combination 128130 is made adjustable so that in this multivibrator it is the parameter of the second control grid that is made variable for varying the width of the rectangular wave 5- appearing in its output. It is the duration of this rectangular wave that determines the duration of the linear portion of the No. 2 sweep. Therefore, multivibrator T--l5T-I0 circuit is adjusted so that the duration of rectangular wave 0-" corresponds to the desired range span on the vemier sweep.

The rectangular wave 5I2 is impressed on the control grid of a triode TI1 which comprises a "single-ended saw-tooth oscillator of No.1 sweep channel. The control grid of T-l1 is connected to the bleeder resistor Ill which impresses positive potential on this grid through a grid resistor 132; therefore, Tl1 is normally fully conductive so that a sweep generating condenser IN is normally kept in a substantially discharged condition. This condenser ia-connected across the output oi T-l'l through a variable resistance I36, the latterbeing shunted by a con- 5 denser 138. ,The plate of T-il is connected to a positive source or potential Ill over a plate resistor H0 andan isolating resistor I42, the latter being shunted to ground by a filtering condenser lll. When the negative rectangular wave l|2 is impressed on the control grid oi- T-ll, it renders this grid negative and T-ll nonconductlve. The voltage across condenser Ill, which was quite low because oi'them drop in the plate resistors as long as T.-il remainediully conductive. now instantaneously jumps up to an intermediate positive potential due to the instantaneous IR drop appearing across resistor 'lli."

Aiter reaching this intermediate potential, condenser 134 begins to charge resulting in a linear portion of the sweep-wave 5-. This initial abrupt start of the voltage -sweep wave 5-" is necessary because it is later impressed on the rotating yoke coils 322 which have considerable inductance, and it is only the voltage of this form that can produce a linear current wave in these coils and 'a linear change in the beam deflecting flux in the oscilloscope tube. Variable condenser I is provided for adjusting the initial wave front oi the voltage wave 6-; the smaller this condenser is, the more instantaneous is the initial rise of the voltage wave. Resistor I26 may be a variable resistor so that proper initial voltage rise may be obtained at condenser 134 Thus, in

order to produce eventually a linear sweep by means of the rotating coils 322, the voltage wave 5-43 may need-some adjustment by means of condenser llll and resistance Ill until the desired linear current saw-tooth wave is obtained. While condenser I38, when varied, may make the sudden voltage rise either more or less abrupt,

variation of resistance I36 will make the ampli circuit of this tube is through a condenser I62, resistance Mil, condenser Ill, grounded bus Ill, ground I50, cells 322, conductor Ilii'and cath-' ode I49. 7

In order to stabilize the central position oi the beam on the cathode-ray oscilloscopethe control grid of T--i8 is also connected to a "clamper" circuit consisting of tubes T--l9 and T20 which act, when conductive, as two variable uni-directional resistances connecting control grid lid to a grounded tap I58 through a bleeder resistor I. These tubes clamp, or hold, the grid potential oi the power amplifier tube Tl8 at a steady,

fixed potential which renders Tls nonconductive when no saw-tooth wave is impressed upon I ground and the control grid of T-l8 at this init. It is essential that amplifier T-I8 always returns to and retains exactly the'same cut-of! potential after impressing the saw-tooth current wave on the coils 322 for two reasons: first, this tube should remain continuously nonconductive during its inactive period so that it does not interfere with the saw-tooth wave 5-I la. impressed on the coils 322 by the second power amplifier T-2Ioi the No. l sweep channel; and, second, T-l8 'rnust always return to exactly the same that when thenext'saw-tooth wave isimpressed 1 lt omen um this wave iron" that fixed cut-oil point thusimpressing on .the deflection coils 122 current saw-tooth waves or the continuously equal That this mustbethe case is not difllcult to understand, since it has been previously stated that the accuracy ot all range determinations depends upon the tact that the sweep always starts from the center on-its outward radial journey, and that the ran e is determined by measuring the-radial distance from this center to .the image oi an echo onth eoscilloscopescreen. Anylackoistability in the circuits 0! T-l. would-immediately result u in a' "wandering zero range poin and inaccurate range determinations. Proceeding nowwith the description oi connections or the circuit, the clamper tubes T- -iland T-2l are to a separate source or potential shown as a bleeder resistor I", an intermediate point "I 01 which is connected to ground. The resistor is by-passed; to ground by'condensers I63 and I65. The plate 0! T-ll is'connected to the positive end of rea sister 1", while the cathode oi T2ll makes a potentiometer type connection with the same re sistorthrough a potentiometer arm Iii connected to a point whichis below the ground potential. The potentiometer arm Iii and the ground tap III are so positioned in resistor 'lllthatsufliciently negative potential is on the control grid'oi the power amplifier tube T -II so as to normally render T-ll nonconductive. I The fact that the positions of the potentiometer arm lit and oi tap I58 determine the biasing potential normally impressed on the control grid I or T-ll will become more apparent from the description oi the l'unctioning cycle of the clamper V circuit. The control grids of 'r-ls and rr-zo are connected in parallel to a coupling condenser which is connected to the positive end or resistor I56. Normally, tubes T--ll and T,2ii are both conductive because oi the mu plate potential initially appearing on the control grids oi these 4 tubes. When this is the case. tube T-2ll becomes conductive and current flows from thelll and t0 agrid resistorlil, the other endofcathode of this tube to the control grid and the plate 0! tube T-2ll. This current at once enables-" tube If-l9 to become conductive so that the two .0! tube T2l to the plate 1;!

stant tube T2ll carries two currents: :one current i is from the cathode oi .T-ZO to' its control grid, this current taking place because, even though the control grid is not veryv far removed from Q the ground potential, the cathode of T2ll is below the ground potential thus making this current possible; the second current is from the cathode of T2ll to its plate, and it is this current that mainly determines the potential between stant. By adjusting the positions of the potentiometer arm "IBI and ground tap "8 on the bleeder resistor I58, the conductivity of T-'-2l| may be controlled thus controlling the potential 70 appearing on the control grid of T-IB, Referring again to the current flowing in series through the two tubes irom the cathode of T2li to the plate of T-IB, it is apparent that the potential impressed on this series circuit byresistor 156 assess:

pedances oi the two tubes. Because or different grid-to-cathode voltages, these impedances wfll v.not be equal, and, therefore, the potential drop ;v; across T-IO will be lower than the potential drop "across T-l8. These grids are always at the same potential to ground, while the cathode of T.-28 is always at a much lower potential to ground than the cathode of T-l8; therefore. T-Ili will be always more conductive than T l 8, the excess current carried by tube T-2ll that is not carried by the plate of -'I-l8 being diverted to the control grid 01' T-28. The entire circuit is so'adjusted by adjusting the potentiometer arm "I andground tap I58 that the voltage drop across tube T28 is considerably lower than the same voltage drop across tube T--l 8, and the grid of tube T-I 8 is at its cut-oil potential when tubes T-ll and T--28 are in their normal conductive state.

' n at this instant, any interference signals ap-Y.

pear across the coupling condenser I52, they=are immediately discharged either across tube T'l8 or tube T-2ll so that the control grid of T'I8 retains its constant potential with respect to ground. when the signals impressed by the coupling condenser 152 are otnegative polarity, they decrease the conductivity of T-2Il and increase the conductivity of T--I8 in proportion to the disturbance created by the condenser and this I change in the conductivities or the tubes immediately restores the potential of the control grid of tube T-ll to its normal value. The same is true when the interference potentials are of positive sign, except that in this case T becomes more conductive and T'l8 less conductive. The control grids of Tl9 and T-2ll are connected 'to the output of T--|5, the first tube of the multivibrator over a coupling condenser I50 which periodically impresses upon these grids the negative rectangular wave 5l2 rendering these grids negative with respect to the cathodes. The circuit oi condenser 168 is: resistor I51,

grounded condenser I85, grounded bus I55, con'-,

denser I28, plate resistor'lll, and condenser 160. When the negative rectangular wave is impressedacrossthe. grid resistor"! and the tubes T--l8 and T28 become nonconductive, they are transformed into high impedance devices, and, therei'ore, current amplifier tube T-i8 ,can now ampliiy the sweep wave impressed upon its control grid at this instant by the sweepgenerator T--l|.

Referring now to No. l sweep channel, it begins with a, diflerentiating network. 188-185 con- 'nected to a diodeTl8. This diode is rendered conductive by .the negative signals sothat its plate output appears as .a' negative signal 5-44. This signal overdrives a nor'mally'c'onductive shaping triode T '2 I. inthe negative direction resulting in a rectangular-pulse 5-45. .It is impressed'on a delayed. multivibrator. consisting or triodes T-22'. .T-28 which correspond to the same type oi'multivibrator, consisting of tubes- T'll and T l8, in the No.*2isweep channel. A rectangularwave 5 l8 appearing in the plate circuit or triode T22 is impressed on thecontrol grid of a saw-tooth generator T2l and "clamperf tubes T-- and T-'-28. The clamper tubes are connected to the control grid of a power amplifier T'2| which is connected to the coils 822. The functioning as well as the connections or these'elements is identical to those in channel readily see that there is no precision delayed multivibrator circuit in No. I sweep channel while thereis one in channel No. 2. Accordingly. No. l sweep channel, and especially its multivibrator T-22-T-23, is so adjusted that the generated sweep corresponds to the maximum range or the system, audits duration as well as its position with respect to the transmitted signal-remain fixed. In the No. 2 sweep channel, while the duration of the saw-toothwave I-ii alsoremains flxed, itstime of occurrence with respect to the transmitted signals may be The voltage waves impressed on the deflection coils 322 of the cathode-ray tube 828 are illustrated at 5-" in Fig.5; the time position of the positive voltage wave may be varied, as illustrated by an arrow appearing above this wave.

- To overcome the negative biasing potential normally impressed on the cathode 812 oi' the oscilloscope tube'824. the intensity grid I is connecwd to the intensity amplifier and mixer I54. and especially to its output potentiometer I58, which lm-f presses a series oi positive rectangular waves onthis control grid simultaneously with the appearance of the linear portions of the saw-tooth waves 5-18 in the coils 822. To accomplish this result, the output of the first tube of multivibrator T22 'T23 is impressed on a normally fully conductive, isolating and inverting .triodefl T-28. Its output 5-20a is impressed on a second amplifier T-28. the cathode of which is coupled to the outputpotentiometer Ill. The

a signal impressed on potentiometer 358 is illus-.

trated at 5'2I in Fig. 5 bythe second rectangular wave. The same type of circuit consisting oi tubes T3ll and T3l is used between the potentiometer 358 and No. 2 sweep channel. Here the negative wave 5- is transformed into a positive wave 5-l8a which appears in the potentiometer resistance 358 after being cathode coupled by a triode T3l-. The final waves impressed on the intensity grid 358 appear at 5-H. By comparing the time relationships between the sawtooth waves 5-i8 and the rectangular waves 5-2l in Fig. 5, one may very readily see that the intensity grid 358 is rendered positive only during the linear portions of the saw-tooth waves. The potentiometer 358 is ordinarily so adjusted that the cathode-ray beam does not quite reach the screen of the cathode-ray tubeifl under normal conditions. Radio locators ordinarily suffer from interference, and this may result in overcoming the biasing potential even when no echoes proper are impressed on the cathode 812 v of the tube. The potential impressed on the in- I tensity grid 356 may be adjusted so that even the interference signals are completely suppressed. but

, I such biasing potential may not be necessarily the Comparing the connections and the .elements in the No. l and No. 2 sweep channels, one may optimum setting'since this may suppress some of the weak echo signals. A better practice. there-- fore, is to adjust the setting of potentiometer 858 so that the interference signals produce only a minor fluorescence on the screen of the oscilloscope tube 324. 1

The outputs of receiver illl, Fig.3 and range marker channel 364 are impressed on the cathode of tube 324 where they overcome the positive bias ing potential impressed on this cathode by the bleeder resistor 318, and 'produce the marker images Illlll and the echo images I888 and Hill, Fig. 10 on the oscilloscope screen. This positive biasing potential is impressed over the following circult: bleeder resistor 318, a conductor I58. a resistorjflii, a double pole-double throw switch I and a conductor Ill. The range marker channel assess:

2i a I consistsof a normallyfuilyeonductive isolating triode T--. which linearly amplifies the rectangular pulses 5-8 impressed upon it by/triode TI. The positive voltage pulses [-22 appearing in the plate circuit of this triode'are transformed into pulses 5-2: by an inverter amplifier T-lf which impresses them on the control grid of triode Tll. Triodes T-li and T-fl comprise a short duty-cycle, self-oscillating multivibrator the frequencyv of which is adjusted by means ola variable cathode resistor "ll so that it generates a series of uniformly spaced rectangular pulses 5-, the spacings between which rep-' resent some chosen distance on the screen of the range oscilloscope. For example, if the full range ofthesystemis350mlles,itmaybeadiustedso that it generates marker signals 5-" at such convenient intervals as l0-or miles. The output of amplifier T-l! phase-synchronizes multivibrator T-3l--T84 insuring simultaneous appearance of the zero range marker signal and 0f the exploratory pulse on cathode I'll of the T-3I. The latter operates as a D. C. restorer which eliminates any positive voltage signals that 'may appear in a coupling circuit 836, 638. The

negative signals 5-41 and 5-25 are impressed on the control grid of the mixer tube T3l, which combines the output of receiver ill with the output of the range marker channel "I, and also limits the amplitude of these signals to a predetermined maximum value illustrated at 5-29.

These signals are impressed on a power amplifier and inverter tube T-JO which transforms them into a series of negative pulses 5-30 and impresses them over a conductor I, a coupling condenser 18!, a double pole-double throw switch 164 a resistor I66 and a conductor I" on cathode I12 of'the cathode-ray tube J24. A second I). C. restorer diode T-40 is connected across resistor Iii which acts as a low impedance path for thesignals which make its plate positive with respect to its cathode thus preventingtheir appearance on cathode Ill.

The power amplifier and inverter T-ll is provided with a switch 642 which connects conductor 0 either to the plate or the cathode of T-IO.

,When switch 642 is in its upper position and con-- .ductor II is connected to the plate of amplifier T-IQ, negative voltage signals are impressed on the coupling resistor I86, and if the double pole- 1 double throw switch I84 is thrown to the left in this case, negative signals will be impressed on cathode I12, which will result in the generation of fluorescent images on the screen of the oathode-ray tube. If it is desired to reproduce the echoes as black images, switches I and 164 may be thrown to their opposite positions, which will at once result in the reversal of the signals impressed on cathode 312, and the eventual reversal of the images-on the screen ofthe oscilloscope ,tube. when the echoes and the markers are reproduced as black images, the potentials impressed on the cathode and the intensity grid IE6 reach the oscilloscope screen and produce an even glow on its face. 7

. The output of the shaping amplifier T-l: is connected over a conductor I80 to'a three-position switch 1.2, the rotating arm of which is connected to a grounded bus 1-. when switch "III is on terminal I. bi-radial sweep operation is obtained but if this switch is connected to the No. I terminal, it grounds the output of the shaping ampiifier-T-II so that No. 2 sweep channel does not generate any saw-tooth wave. With the shaping amplifier T-i! grounded. the oscilloscope tube) reproduces only the No. i sweep and the associated signals. This type of operation may be called as a one sweep channel operation. and, therefore, resembles a conventional mode of operating the P. P. .1 systems, exceptthat every other exploratory pulse and the-resulting echoes do not appear on the oscilloscope screen. The same mode of operation may be obtained forNo. 2 sweep by turning switch 182 to terminal No. 3, thus grounding ,the output ofthe shaping amplifier T-Il. Aspreviously mentioned in this specification, the rotating speeds of antenna 308, Fig. 3, may be in the order of from one to twenty revolutions per minute, or

. even higher, but it is more usual to encounter rotational speeds in the order of l to 2 R. P. M.'s

rather than the higher limits. when the antenna rotational speeds are in the order of 1 to 2 R. P. M.s and the keying rate of transmitter 304 is in the order of 300 cycles ,per second, very satisfactory results are obtained on the oscilloscope screen without any overlappin of the biradial images when the retentivity or this screen is in the order of P| screen, R. M. A. code. However, as the rotational speed of the antenna isincreased above 2 R. P. M. with the keying rate remaining constant, because of the relatively high retentivity of the P--'l screen, considerable glow ends of the sectors up to the time of appearance of the following sector resulting in a simultaneous reproduction of signals by the two channels over the same screen sectors. This would obviously result in the confusion of the images on the oscilloscope screen. The three position switch I8! is provided for eliminating this confusion. By setting this switch to the previously mentioned positions, either of the two channels may be completely eliminated thus avoiding the above-mentioned overlapping of the images.

In Figs. 3 and 12 a sector scanning arrangement is disclosed, which enables one to scan either a 180 sector, or a smaller or larger sector, de-

pending upon the configuration of the conducting segments of a commutator provided for this purpose. This sector scanning arrangement becomes desirable when the angular speed of antenna is greater than 2 R. P. Provisions are also made for slowly rotating about the center of the oscilloscope screen the scanned sector at the rotational speeds less than 2 R. P. M. The

latter arrangement enables one to retain all theadvantagesof the bi-radiai sweep display through 360 of azimuth at the antenna rotational speeds which are higher than 2 R. P. M.

Referring to Figs. 3'and 12, the intensity grid I of the cathode-ray tube 324 is connected toa positive source of potential 316 over conductors 3", I", 382, brushes 385, 381, 39!, and slip rings 806,188 and 390. The slip rings may be shorted by means of a knife switch 393 thus connecting the intensity grid to the bleeder resistor tol 'igflmoreinparticuhntbeieo'segment.

I is rotated around the longitudinal center line 01' the oscilloscope tube III, which is represented as a center point I". in Fig. 12. Segment I is" mounted on the rotating ring 32., which also acts as a mounting means for the deflec ion coils I22, and, therefore, is rotated by the "Selsyns" Ill and I2l, Fig. 3. Brush Ill, which is mounted on the slip ring litmakes an'electrical contact with segment Ill. The slip ring I is mounted on a gear l2, the latter being connected through a worm gear. I2 to a motor I208. The slip ring IIl,-which revolves thesamecenter l2le,andisalsomountedonring 320, is electrically connected through brush "I a continuous sequence. ii the rotation of -24; sectors-ctc.,will

section ahng line A-A of Fig. 10. andl'ig. 14 being a fragmentary longitudinal section of Fig.

310. Thiadial and its grating may be used with P. P. I. oseiiloscopes when 'no marker circuit is and conductor 392 to the intensity grid 38'. Ring l0. and segment ill are interconnected by means oi a conductor ill. When switch III is closed, the commutating arrangement is shorted,and

rid 38. is connected directly to source 310 over:

switch I. With switch 303 closed, 360" azimuth -scanningisobtained.

Whenthe angular speed of antenna III is above a certain limit, or only a sector scanning is desired, it to the tube when the antenna i plish this, switch III is opened. and the sector scanning arrangement put into operation. When switch! is opened, the circuit of the intensity grid ill is: conductor I92, brush "I, ring "I.

conductor "9, segment at, brush 3", ring I, brush I, conductor 3 and bleeder mister I". Since conducting segment Illrevolves at thesam'espeedandisorientedinthesamedirection as antenna Ill, it follows that the intensity grid III will receive the necessary pofltive potentialaslongasbrushlll remainsontheconduc-- tive segment I. When this contact is broken by an insulating segment l2ll,- cathode-ray tube 324 becomes extinguished, and remains extinguished until brush ill make an electrical conextinguish pointing in the direction of the undesired sector. To accom- 'oitherangescale circles,andarangereierence .circle III. thepurpase'oi' which will be'described available. or when amapo! surveillance is preferred. Although the grating is-described here in connection with its adaptation to a P. P. I. oscilloscope, it is apparent that the structure has a much wider utility, and may be usedwherever an illuminated diai'with a scale is desired. The'dial consists oia' curved disc llll which matches the curvature of the oscilloscope screen and is superimposed directly over it. With the exception of the azimuth scale, one circular groove llli representing one later in this specification, no complete etched scalesareillustratedinanyo! the figures.

The lighting arrangement of this dial plate is illustrated more fully in Figs. 13 and 14. A disc ljl2l flts with its outer edge into a groove i l22 in a split ring ,l82llO25, Disc I02! and split ring lure-10:5 are made of a transparent resin, such as acrylic resins which are the solid .iorms oi the .polymetric, esters oi acrylic and methtact once more with the conducting t 388.

One of the advantages of this system resides in the iact that sector scanning posible without resorting to a sudden reversal of rotation of antenna 3" at both ends of the sector,

thus avoiding the imposition of high acrylic acid. Polymethyl methacrylate (typical trade names are Lucite and Crystallite) is an -especialiy suitable material. Two metal sockets I126 and I028 join'the ring at "32 and II",- these sockets holding electric bulbs i030 and It". The ring itself is surrounded by a rubber casing I. and me so that light entering the ring at "Hand i842: is prevented from illuminating anything else but the grating. Springs It, is,

and clamping rings i045, INS are provided on the electric bulbfsocsets for holding the grating on a frame supporting the cathode-ray oscilloscope tube 324; A light emanating from the bulbs "3|,

- llil enters the'rings i826, il'liat their split V portions its, i042, and is conducted by the rings stresses on the antenna and its mount..- When this type of sector scanning is-used, No. I sweep is reproduced over one sector and No. {sweep over the opposite sector of the oscilloscope screen. The retentivity oi the oscilloscope screen, the

rate 0! keying, as well as the rotational speed oi antenna 382, when this p 01 operation is used, are such that-images oi suflicient brilliance areordinarilyretainedonthepescreen although the tube itself is operated only during one-halt oi the revolution 01' the antenna.

Ii, with such sector scanning; it becomes desirable to gradually shift the active sector so that 7 it scans the entire 360 at relatively slow speed,

motor l2 may be started resulting in the rota-- tion-of gear l2, ring 388, and brush Ill. The

rotation of ring 88 6 changes the relative speed oi brush ill with respect to the conductive segment I, and this produces gradual angular rotation of the active, selected sector about the center of the oscilloscope screen. For example, it -the initial scanning were restricted to the northern 180 sector, the scanned sector may be gradually rotated. either in a clockwise or countcrclockwise direction, depending upon the direc-v tion of rotation of ring 386. Thus, first a northern sector, then eastern, souththrough the groove i022 into disc "20, thus internally illuminating the disc over its entire surface. U

Light confined to disc i020, upon striking the et'chedportions "2| and I023, which are in this case etched on the inner surface or disc illl for avoiding the between the etchings and the oscilloscope screen. illuminates the etchings ,which appear as brightly illuminated, glowing length-frequency scales should be placed. on the outer surface of disc, "20, i. e. the surface facing the reader or the dial. To accomplish a uniform distribution of light over the entire area or disc "2!, the surfaces oi grooves lll22 and oi the peripheral edge oi disc I02. have a finish of progressively increasing degree of roughness, the

from the m of light. m light-en it in surfaces-ll and ill! have a polished finish.

am'l

ofbright spots llll'appearingontherespective n is obvious um the r; a r. sylicm illustrated in Figs. 8, 4, 8 and 'I will function quite well without any grating since theimarker circuit provides sufficient range scale for identifying the range of the objects. The angular azimuth scale, how

ever, cannot be dispensed with, and must be used irrespective of the presence or absence of the central range scalegrating.

The functioning of the P. P. 1. system should and potentiometer 1 ,of the saw-tooth oscil-v lator tubeT-ll are adiusted until the sawsw psrand if the full range is, for example, a 150 mile range, oi therange marker generator isso adjusted so as mile markers potentiometer 121 of the multivibrator tube T-Il tooth waveand radius I'll-"II, Fig. 10, ends be apmnt from the description thus'far given, I

and only a brief summary of its operating cycle is -n for its completion. Upon starting of the entire system illustrated in Figs. 1, 2 and 3, driving motor fit is disconnected from an'A. C. source at that instant when the lobe axis of the antcnna array 308 points directly north. Upon proper orientation of the antenna, the indexing wheel ails used for positioning the yoke coils "I so that theline lllll, lflif, Fig. 10 formed by the two sweeps also points in the northerly dipulse signal from an outside source is impressed on conductor ll I, video amplifier and mixerjll, and cathode I12 of the cathode-ray tube 324. The pulse frequency is chosen to produce the desired standard marker spacings on the oscilloscope screen, which are then used for adjusting the marker signals lllllt generated by the range markerchannel llll, Fig. 4. If the range marker channel frequency is properlyadjusted, the bright spots I 00 produced on the oscilloscope screen by the range marker channel and the If only sector scanning is desired, switch 393,

Figs. 3 and 12, isopened, thus transferringjcontrol over the potential impressed on the intensity standard frequency pulses will be uniformly spaced with respect to each other over the entire sweep. If the range marker .channel generates a frequency which differs from the frequency generated by the standard frequency generator,

the bright spots appearing on the oscilloscope screen will have nonuniform spacings, and this may be used for adjusting the frequency of the range marker channel by adjusting resistance 630, Fig. 6 connected in the cathode circuit of the multivibrator T.38T3l until uniform,

spacing of bright dots is obtained. To make the adjustment of the standard range marker channel! more convenient, a phase shifter may be interposed between standard frequency source and conductor Ill so that complete coincidence between the bright dots produced by thesetwo sources of signals is obtained when the frequency of the range marker channel is equal to the standard frequency. w I

After the range marker channel has been adjusted, the durations of the duty cycle waves 5-", 5-42, and the amplitudes of the saw-tooth waves 5-410 and 5-4311 generated by the No. 1 and No. 2 sweep channels are adjusted by adlusting potentiometer resistors 121, 128, 140 and "I appearing in the grid circuits of the multivibrator tubes T-23, T|6 and in the output circuits of the saw-tooth oscillator tubes T-l 1 and T-2l. Since the frequency of the range marker channel GM has now been adjusted, the range reproduced on the oscilloscope screen can be very readily obtained by counting the number at the 15th dot, and this'dot screen; The same procedure is followed in connection with the No. 2 sweep channel. It is obvious that the saw-tooth oscillator and its as-' sociated circuits will need additional preliminary adjustments for checking. the linearity oi the saw-tooth wave generated by these channels. These adjustments, however, are very well known to those skilled in the art, and for that reason ,need not burden this disclosure. with the markers and sweep channels adjusted, the output of receiver Ill is impressed on the oscilloscope J tube and, with only the interferencesignals impressed by the receiver, the potentials impressed on the intensity grids I8... 356 and cathode 312 are adjusted to cut-ofl potential of thecathoderay beam; Upon the completion of vthis last ad justment, driving motor I" isconn'ectedto the A. C. source of potential, and the entire system is made to scanthe desired field. If a 380' scanning is desired with both sweeps appearing on the oscilloscope screen the three-position switch 182 is placed on its terminal No. I so that both 7 sweep channels remain active and switch! is closed so that sector scanning distributor is shunted. At any desired instance one of the channels may be rendered inactive by operating switch 182 to its position No. I or No. l so-that either the main range or the auxiliary Vernier range only appear on the oscilloscope screen.

grid 380 of the cathode-ray tube 324 tosector sea and ring m. It gradual changing of the scanned sector is desired for obtainin 360 azimuth scanning, motor I208 is started, which results in the rotation of the conducting ring 386 and rotation of brush 381. when this is the case the scanned sector itself is slowlyrotated-at a speed corresponding to the speed of rotation of brush 381. This speed should be lower than the rotational speed of the antenna. The functioning of the oscilloscope.circuit itself is as follows: if the oscilloscope is connected to a synchronous radio, locator such as the one illustrated in Fig. 1, synchronizing. oscillator I0 is used for controlling the'timing of all t'ransmitter and receiver channels, the oscilloscope circuit being a component of the receiver channel. For

accurate azimuth determinations the ,sweep must always point in the same direction as the axis of the antenna array beam. This require ment is satisfied, as it has been explained in connectionwith Fig. 3, by pointing antenna array directly north, or in any'other known direction and by adjusting the angular position of the cathode-ray beam on theoscllloscope screen by means of the indexing. wheel I" so that it points in the same direction; :Since from; then on the antenna array and the yoke coils 322 New" appears'in the proper place on the. outer periphery of the per each cycle of the sinusoidal wave.- These rectangular pulses are then transformed into the rectangular waves -4 by means of the multivibrator circuit.T-0T-'I, Fig. 6 which is used for generating the rectangular lator '1'l and the multivibrator circuits T-II- T-fl in No. I sweep channel and Tl3T- ll in the No. I sweep channel are for the sole purpose of generating a single rectangular pulse in one sweep channel during one cycle of the sinusoidal wave. and then an identical rectangular pulse in the other sweep channel during the next cycle of the sinusoidal. wave. The timing of these rectangular pulses 5-! and Iii' depends upon the timing of the sinusoidal wave, and, therefore, these pulses 'will always follow any change in frequency or of the sinusoidal wave; In No. I sweep channel the rectangular pulse I-ll is used for timingthe generation of the saw-tooth wave il| by controlling the delayed multivibrator T--22, T-Ii', the output of which in turn controls the operating cycle of the saw-tooth oscillator T24. In this sweep channel the timing of the saw-tooth wave I--l| remains fixed with respect to the transmitted signalso that both appear simultaneously at the cathode-ray tube 324, which satisfies the second requirement, and namely, that the sweep must always start at the time of transmitting an exploratory pulse. In No. 2 sweep channel, circuits must be provided for changing the time of appearance .of the saw-tooth wave in the coils Ill, and for accomplishing this result a precision delayed multivibrator circuit T-IITI| is provided which enables one to delay the generation of the saw tooth wave any desired time ai'ter the transmittal of the exploratory pulse by merely adjusting the potential 1m on'the control grid of the precision delayed multivibrator. The remaining elements of the No. 2 sweep channel are identical to thesame elements in No. l sweep channel; they consist of a delayed multivibrator circuit T-jlS-Tl0, a saw-tooth oscillator T-l,|, and a power amplifier T-il with the circuit Tls-T2l. The precision delayed multivibrator is so adjusted that any desired portion of the full range reproduced on No.

lsweepmaybereproducedontheNoJsweep.

Its potentiometer is calibrated in proper linear uniis, such as yards, miles, or kilometers-so that theentirerangeofthedesiredechomaybedetermined by'readin g the setting of potentiometer.|0la ndaddingtothisreadingtherange reading appearing on the vernier sweep scale.

Normally, when this mode of-range is used, the precision delayed multivibrator potentiometerissocalibratedthatthe desiredmarkpulsI-J 'inonesweepchannehandasimilarrectangular am s .desireddistance-.andthedistancetothedesired echo is determined by either adding orsubstracting the oscilloscope screen range indica- Forexample." let it be assumed that the full range of thesystem'is150milesandthereare10mile markers available. Suppose the desired echo is located between the th and 11th markers on the main sweep, indicating that its distance is more than 100 miles. The operator-may select either the 10th or the 11th marker for position ing of this echo on the vernier sweep byturning the potentiomcterdial either to 100" or "110."

Suppose that the vernier sweep has-a 30 mile range. If 100" were placedto the midway position on the vernier sweep, the echo'would' be reproduced between this midway marker and the outer portion of the sweep. To obtain the range in this case, the operator would the potentiometcr dial, which reads and addthe estimated distance perceived from noting the positionoftheechohetween the lothandthe 'llth markers. If it is midway between them. the total range wouldbe miles. If the operator had chosen the 11th marker in the. previous case, the echo would appear between the 11th markerandtheinnerportionoftheswecp. and itwouldbeforhimin'thiscaseto subtract 5 miles from the reading on the potentiometer scale.

Thistypeofrangedeterminationhssitslimitations since it involves reading of the potentiestimating the additional range of ometer scale. the echo on the vernier sweep, and mentally adding the two by'the operator. Moreover, in order reading is taken by the operator.

to obtain accurate range determinations with mode of range determination involves four sepasteps. and the step involving adding of the is an vulnerable one whichisapttoresultintheerroneousrange determinations, delay accurate range readings. and tax the operator's abilities to an undue extent; To avoid this diillculty, a more reliable range determination method consists of the following procedure. The grating is provided with a range reference circle I050. which is preferably positioned midway between the center point I002, Fig. 10, and the outer periphery of the oscilloscope tube defined by the azimuth scale in' Fig. 10. This range reference notch which sometimes replaces the hair line.

This type of range determination is disclosed. for example, in an application for patent by William A. Huber and William T. Pope, Serial No. 500.5118, iiled on October 19, 1943. and entitled "Radio Object-Locating System." The grid potentiometer II! is then calibrated so that its scal sivcseto etheentircrangereadingwnen 

